Automatic starting arc lamp



July 21, 1970 M. J. SCHARF AUTOMATIC STARTING ARC LAMP Filed Oct. 1, 1968 .JNVENTOR MAICE H F BY a M n.

ATTORNEY United States Patent O 3,521,114 AUTOMATIC STARTING ARC LAMP Maurice J. Scharf, Fostoria, Ohio, assignor to Union Carbide Corporation, New York, N.Y., a corporation of New York Filed Oct. 1, 1968, Ser. No. 764,103 Int. Cl. HOSb 31/30 US. Cl. 31434 7 Claims ABSTRACT OF THE DISCLOSURE Means are provided for improving initial are striking in an are light source. An annular refractory tube is positioned between electrodes and in contact therewith. When current is caused to flow through the tube an arc is struck between electrodes and the tube is automatically ejected. With the use of such a tube, no movement of the electrodes is required to strike an arc, thus eliminating the need for manual manipulation by an operator.

FIELD OF THE INVENTION This invention relates to light sources and more specifically to a means for improving initial arc striking in a carbon electrode light source.

DESCRIPTION OF THE PRIOR ART Arc carbon electrodes are employed in devices wherein the light which is in the crater region of a positively polarized carbon electrode is employed as a source of illumination. Such devices include search lights, motion picture projector lamps, solar simulation apparatus and the like. While these devices function extremely well in operation, starting the arc is sometimes a time consuming task, particularly if manual manipulation of the electrodes is employed.

To start such are lamps generally requires the application of a high voltage pulse to break down the dielectric material interposed between the positive and negative electrodes. To offset this requirement, the electrodes are initially brought together so that only a small gap must be overcome, and after the arc is struck, the electrodes are slowly drawn apart until the desired gap is achieved. Obviously, this procedure must be carried out with care since unsteady movements may cause the arc to be extinguished.

To overcome the problems associated with such a procedure, several mechanisms designed to provide a self starting feature have been employed in arc lamps. For

example, US. Pat. 3,256,459 discloses an arc lamp in which a conductive fusion bridge spans the gap between electrodes and forms a low resistance electrical path therebetween. The fusion bridge is shaped such that its cross sectional area progressively increases axially in the direction of one or both electrodes. A starting voltage vaporizes the bridge from the minimum cross-sectional area outward toward the electrodes thereby creating a progressively larger gap. Such a construction is costly, has a poor shock resistance, and requires expensive support and alignment equipment.

Another self starting arc lamp is described in US. Pat. 3,377,497 wherein a conductive wire of substantially uniform cross section is used to bridge the gap between electrodes. The wire is secured to the electrodes by being spot welded to the electrode portion immediately following the tapered arc end. One or more accommodation slots or grooves are cut into the peripheral surface of the end portions of the electrodes so that the bridgewire is axially suspended between and firmly secured along the arc end electrode sections. The wire is of a diameter sufficiently small to permit it to fuse or burn out before the 3,521,114 Patented July 21, 1970 are lamp is damaged by the initial current flowing therethrough. While this construction is somewhat successful, it also has several disadvantages. Much time and labor is expended in attempting to affix the wire to the electrodes since both welding and machining operations must be carried out. In addition, damage to the arc lamp can be appreciable if careful wire manufacturing tolerances are not observed.

Other self-starting arc lamp devices have been developed but all are either too complex and thus quite costly or require excessive labor effort to secure or assemble the self starting component to the electrodes.

It is the primary object of this invention therefore to provide a self starting arc lamp which is easily assembled, inexpensive to manufacture, and is automatically operated.

SUMMARY OF THE INVENTION Broadly, the objects of the invention are accomplished by the use of an annular refractory tube which is positioned between and in contact with the arc electrodes. The tube is easily attached to the electrodes and is automatically ejected when the are is struck. With the use of such a tube, the electrodes may be spaced a proper distance, and no further movement is needed to strike an arc. Thus, manual effort by an operator is not required.

The tube is preferably composed of a major amount of a carbonaceous material such as carbon or graphite since this material provides good electrical conductivity and excellent thermal resistance. This latter property permits the tube to withstand the extreme temperatures in the arc region so that the tube can be used again after being ejected from the region of the arc.

The manner in which the tube may be afiixed to the electrodes is an important advantage of this invention since a minimum of assembly time is employed. Because the tube is hollow, it is readily placed over the arc end of the electrode and this placement is virtually independent of the shape of the electrode since the tube can be fabricated with an inside diameter large enough to fit around such electrodes. However, since electrodes of this type are often provided with a tapered end portion, the tube can be situated over the pointed segment of the tapered portion without difficulty. In addition, a recess may be provided in one or both of the electrodes at the arc end and the tube can be positioned partially within the recess and supported by the lower lip of the recess. In this manner, the tube is quickly positioned on but not rigidly secured to the electrodes and spans the gap between electrodes. The contact between tube and electrodes is suflicient in this assembly to provide a low resistance path for electrical current. Therefore, when a voltage is applied to the electrodes, current passes through the tube and between electrodes. The initial surge of current causes local arcing to occur along the inner walls of the tube and across the dielectric gap between electrodes, that is, down the center of the tube. An arc is thereby struck almost immediately after the initial current surge passes through the tube walls. The breakdown of the dielectric, which is usually air, is accompanied by an expansion of the air along the path of the arc. This expansion exerts a force on the tube sufficient to force it from its loosely held position on the electrodes and causes the tube to drop away. This phenomenon occurs automatically and Without operator assistance thereby enhancing the operation of the system.

FIG. 1 is a perspective view of part of an illumination lamp employing a refractory tube for self-starting;

FIG. 2 is a plan view in cross section of a refractory tube suitably employed in the invention;

FIG. 3 is a front elevation view of the tube in FIG. 2; and

FIG. 4 is a front elevation view of another refractory tube suitable for use as a self-starting component.

Referring to the drawing, there is shown in FIG. 1 an arc lamp comprising an electrode 12 which rests in holder 14 and a second electrode 16 spaced from electrode 12 and positioned with its longitudinal axis at an angle relative to the axis of electrode 12. A recess 18 is provided in electrode 12 while electrode 16 is equipped with a tapered end portion 20. A refractory tube 22 is placed with one end over tapered end portion 20 which fits in the hollow tube space 24, and the other end is placed in recess 18. Recess wall 26 supports the tube 22 and also provides good electrical contact between the electrode 12 and tube 22.

In the operation of the system, the electrodes 12, 16 are initially spaced a desired distance and positioned to form an angle of up to 75, usually about 55. Tube 22 is slipped over tapered end 20 of electrode 16 and into recess 18. A voltage is applied to electrodes 12, 16 and since the tube 22 electrically connects the two electrodes, at current flows through the tube walls. Local arcing occurs within the tube and the air dielectric is broken down with the result that an arc is struck between electrodes 12, 16 through the hollow space 24 of the tube 22. The tube 22 is ejected from the region of the arc by the force of the arc and expanding air.

The refractory tube 22 is more clearly illustrated in FIGS. 2 and 3. The tube is provided with a relatively thin wall 28 in the preferred embodiment because electrical resistance is thereby increased and, in addition, the initial positioning of the tube is thereby facilitated. The wall thickness is preferably between about 4 percent to about percent of the outside diameter of the tube. Although the tube is illustrated as being cylindrical in shape, generally any shape which will provide a suitable path for the arc to be struck is acceptable. As shown in FIG. 4, for example, a tube 30 having a hollow center space 32 is also provided with 'an opening 34. The opening facilitates placement of the tube on certain electrodes, such as two tapered electrodes, and aids in the.

ejection of the tube from such electrodes when the arc is struck.

The following examples further illustrate the principles of the invention.

EXAMPLE I A positive carbon electrode 22 inches long by 13.6

millimeters in diameter was positioned at an angle of,

57 with respect to a negative copper coated carbon electrode measuring A inch in diameter and 9 inches in length. The electrodes were present with an air gap of ,5 inch therebetween. A carbon tube inch long and having an inside diameter of 0.195 inch with an outside diameter of 0.242 inch was placed at one end over the tapered negative electrode and at the other end on the lower wall of the positive electrode recess. A voltage of about 60 volts and a current of 125 amperes were applied to the electrodes and through the tube causing an arc to be struck and the tube to be automatically ejected. The voltage and current were thereafter main tained at the same level.

EXAMPLE II Same as Example I except that the initial gap between electrodes was inch, and the voltage applied was volts with a current of amperes.

EXAMPLE III A positive copper coated carbon electrode measuring 9 millimeters in diameter and 14 inches long was set at an angle of 0 relative to a negative copper coated carbon electrode 8 millimeters in diameter by 9 inches long. An arc gap of .275 inch was bridged by a carbon tube 0.195 inch inside diameter, 0.242 inch outside diameter, and inch long. An arc was struck and the tube was ejected with a voltage of 45 volts and a current of amperes which were also used tomaintain the arc.

It will be appreciated that the foregoing examples are merely illustrative of the invention and a wide variety of modifications of the invention are possible. For example, the tube may be composed of other refractory materials such as coke, graphite, and combinations of various forms of carbon. In addition, various electrode configurations embodying recesses and tapered end portions can be employed.

What is claimed is:

1. In an arc lamp comprising two electrodes with a gap therebetween, the improvement which comprises an electrically conductive refractory tube having a hollow center portion extending therethrough, said tube being positioned in said gap between said electrodes and being in direct contact with said electrodes, whereupon with the passage of current through said tube an arc is struck between said electrodes in said hollow portion.

2. In an arc lamp comprising two electrodes in a spaced relationship, one of said electrodes having a tapered end portion and the other electrode having a recessed end portion, the improvement which comprises an annular electrically conductive refractory tube in direct contact with said electrodes, said tube having a hollow center portion and being positioned with one end in said electrode recessed portion and the other end being placed over said tapered electrode section, said tube being positioned such that upon application of electrical energy to said electrodes current passes through said tube to thereby strike an arc between said electrodes and to thereby automatically eject said tube from said electrodes.

3. The are lamp of claim 2 wherein said electrodes are composed of at least a major amount of carbon.

4. The are lamp of claim 2 wherein the longitudinal axes of said electrodes form an angle of up to about 75.

5. The are lamp of claim 2 wherein said tube is composed of a carbonaceous material.

6. The are lamp of claim 5 wherein said tube is provided with an opening which extends along one wall thereof to facilitate placement and removal from said electrodes.

7. The are lamp of claim 5 wherein the wall thick ness of said tube is between about 4 percent and about 35 percent of the outside diameter of said tube.

References Cited UNITED STATES PATENTS 2,607,024 8/1952 Marwell et al 31434 X 3,274,427 9/1966 Paquette et a1. 314-34 3,452,236 6/1969 Beese 31533l X BERNARD A. GILHEANY, Primary Examiner R. N. ENVALL, IR., Assistant Examiner 

